MODELING MAGNETIC STRUCTURE IN 2D VAN DER WAALS MATERIALS WITH NEUTRON DIFFRACTION

Abstract

In this thesis the magnetic structure was determined using neutron diffraction for threerelatively novel van der Waals (vdW) crystals, Fe3GaTe2, NiP(S1−xSex)3, and FeP(S1−xSex)3. Fe3GaTe2 was found to be a self-intercalated ferrimagnet with interstitial iron sites between the vdW gaps. The magnetic space group was determined to be P63/mm′c′, which implies that a collinear antiferromagnetic arrangement exists among the interstitial iron site and iron sites in the telluride layers. Mixed anion NiP(S1−xSex)3 was observed to be an antiferromagnetic compound with a magnetic space group of P1 with the moment oriented in the ab-plane. The addition of Se to NiPS3 results in a reduction in the total magnetic moment with it hovering between 1.0 - 1.5 µB. Mixed anion substitution was found to have a greater affect on FePS3 and FePSe3. One additional antiferromagnetic magnetic phase besides the antiferromagnetic parent phase was observed for mixed anion FePS3 and for mixed anion FePSe3. Interestingly, the total magnetic moment for the new observed phases imply that the octahedral-coordinated Fe atoms form a low-spin configuration for a d6 metal.